Add and Remove Host Entries

This is a quick script I’ve used to add and remove hosts entries to the windows hosts file. It ignores commented lines (lines starting with a hash (#)), and it also doesn’t validate the format of the host or IP address so use with care!

Add And Remove Host Entries

cscript.exe hosts.vbs “Add” “10.10.10.10” “example”
cscript.exe hosts.vbs “Remove” “10.10.10.10”

Option Explicit

Const ForReading = 1
Const ForWriting = 2
Const ReadOnly = 1

'Usage
'cscript.exe hosts.vbs "Add" "10.10.10.10" "example" 
'cscript.exe hosts.vbs "Remove" "10.10.10.10"

If (wscript.arguments.count < 2) Then
	'need a verb, host as a minimum
	Wscript.quit
End If

'Add/Remove
dim inputAction : inputAction = wscript.arguments(0)
dim inputIPAddress : inputIPAddress = wscript.arguments(1)
'host can be blank if removing
dim inputHost
if (wscript.arguments.count > 2) Then
	inputHost = wscript.arguments(2)
End If

dim oFSO : Set oFSO = CreateObject("Scripting.FileSystemObject")

dim objShell : Set objShell = CreateObject("WScript.Shell")
dim strSystemRoot : strSystemRoot = objShell.ExpandEnvironmentStrings("%systemroot%")
dim pathToHosts : pathToHosts = strSystemRoot & "\system32\drivers\etc\hosts"

'make changes in memory first - we need to open it in write mode first otherwise we get 'Bad file mode' error
dim hostsFile : Set hostsFile = oFSO.OpenTextFile(pathToHosts, ForReading, true)
'get original read from file.  We'll amend hosts in memory until we commit changes at the end
dim hostsContent
If Not hostsFile.AtEndOfStream Then hostsContent = hostsFile.ReadAll

dim hostEntry

if (inputAction = "Add") Then
	hostsContent = AddHostEntry(inputIPAddress,inputHost)
End If

if (inputAction = "Remove") Then
	hostsContent = RemoveHostEntry(inputIPAddress)
End If

hostsFile.Close()

'set attribute to read/write if readonly
dim objFile : Set objFile = oFSO.GetFile(pathToHosts)
If objFile.Attributes AND ReadOnly Then
    objFile.Attributes = objFile.Attributes XOR ReadOnly
End If

'then write changes to actual file
Set hostsFile = oFSO.OpenTextFile(pathToHosts, ForWriting, true)
hostsFile.Write hostsContent
hostsFile.Close()
    
Function RemoveHostEntry(ipAddress)
  
	dim objRegEx : Set objRegEx = CreateObject("VBScript.RegExp")
	objRegEx.Pattern = "^(?!#)(" & ipAddress & ")(\s|\t)+"

	dim strNewContents : strNewContents = ""
	
	dim hostsContentLines : hostsContentLines = Split(hostsContent,vbCrlf)
	For each hostEntry in hostsContentLines
		If NOT objRegEx.Test(hostEntry) Then	
			strNewContents = strNewContents & hostEntry & vbCrLf		
		End If
	Next
	  
	'remove last carriage return	
	If Right(strNewContents, 2) = vbCrLf Then
		strNewContents = Left(strNewContents, Len(strNewContents) - 2)
	End If
	
	Set objRegEx = Nothing
	
	RemoveHostEntry = strNewContents

End Function

Function AddHostEntry(ipAddress, hostName)
  
	dim objRegEx : Set objRegEx = CreateObject("VBScript.RegExp")
	objRegEx.Pattern = "^(?!#)(" & ipAddress & ")(\s|\t)+"

	dim strNewContents : strNewContents = ""
	dim hostnameExists : hostnameExists = false	
	
	dim hostsContentLines : hostsContentLines = Split(hostsContent,vbCrlf)
	For each hostEntry in hostsContentLines
		If objRegEx.Test(hostEntry) Then
			hostnameExists = true	
		End If
		strNewContents = strNewContents & hostEntry & vbCrLf
	Next
			  
	If Not hostnameExists Then
		strNewContents = strNewContents & ipAddress & vbTab & hostName 
	End If
	
	'remove last carriage return	
	If Right(strNewContents, 2) = vbCrLf Then
		strNewContents = Left(strNewContents, Len(strNewContents) - 2)
	End If
	
	Set objRegEx = Nothing
	
	AddHostEntry = strNewContents

End Function


Set hostsFile = Nothing
Set objFile = Nothing
Set oFSO = Nothing
Set objShell = Nothing